This application is based on Japanese Patent Applications No. 2001-372257 filed on Dec. 6, 2001, No. 2002-27657 filed on Feb. 5, 2002 and No. 2002-296154 filed on Oct. 9, 2002 the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a fuel injection system for an internal combustion engine. More in details, the invention relates to a fuel injection system for executing multi-injection including preceding injection and succeeding injection.
2. Description of Related Art
JP-2001-140689A discloses an accumulator fuel injection apparatus. According to an accumulator fuel injection apparatus, fuel is pressurized by a pump and pressurized fuel is accumulated in a common rail. High pressure fuel is distributed into a plurality of injectors from the common rail. The injector injects fuel into a combustion chamber. The accumulator fuel injection apparatus is referred to also as a common rail fuel injection apparatus.
In the case of accumulator fuel injection apparatus, a command injection amount (Q) is calculated by an engine revolution speed (NE) and an accelerator opening degree (ACCP), a command injection timing (T) is calculated by the engine revolution speed (NE) and the command injection amount (Q), electricity conducting time (command injection time: TQ) of an injector drive signal to the injector is calculated by fuel pressure (fuel pressure: Pc) in the common rail detected by a fuel pressure sensor and the command injection amount (Q), and a nozzle needle in the injector is opened by applying the injector drive signal in a pulse-like shape to an electromagnetic valve of the injector until finishing the command injection time (TQ) from the command injection timing (T) to thereby control the injection amount and the injection timing of fuel injected to supply from the injector into a respective cylinder of the engine.
Further, in order to deal with regulations of exhaust gas and noise in the accumulator fuel injection apparatus in recent years, specifically, with an object of reducing noise or vibration and promoting an exhaust gas performance of the engine by carrying out stable combustion from start of main injection, there is executed multi-injection (multi-injection) for carrying out small amounts of a plurality of times of preceding injection (pilot injection) before the main injection (main injection) which can constitute engine torque at a vicinity of top dead center. The multi-injection aims to restrain noise or vibration and promote the exhaust gas performance of the engine and the like in an injector of a specific cylinder of the engine by carrying out twice or more of multi-injection by opening the nozzle needle twice or more by driving the electromagnetic valve of the injector twice or more in the compression stroke and the expansion stroke of the engine (for example, once or more of pilot injection and main injection, or once or more of pre-injection and main injection, or pilot injection or pre-injection and main injection and after injection, or main injection and once or more of post-injection).
However, the injector mounted to the respective cylinder of the engine is constructed by a constitution in which by controlling back pressure of a command piston reciprocally moved in cooperation with the nozzle needle by opening and closing the electromagnetic valve, fuel pressure in a fuel storage provided at a surrounding of the nozzle needle, that is, fuel pressure operated in a direction of opening the nozzle needle overcomes urge force of a spring, etc. operated in a direction of closing the nozzle needle to thereby open the injector and therefore, after the elapse of predetermined injection delay time from starting electricity conduction to the electromagnetic valve of the injector, the nozzle needle is opened, further, after the elapse of predetermined injection finish delay time from finishing electricity conduction to the electromagnetic valve of the injector, the nozzle needle is closed.
Here, during the compression stroke of the engine, in carrying out multi-injection for carrying out once or more of small amounts of pre-injection or pilot injection prior to main injection by executing a plurality of times of electricity conduction to the electromagnetic valve of the injector, there poses a problem that by a change in the fuel pressure in the common rail which is brought about by pre-injection or pilot injection executed prior to main injection, the injection start delay time is shortened or prolonged to thereby bring about a variation in an injection amount relative to an aimed injection amount.
Hence, during the compression stroke of the engine, in executing multi-injection for carrying out once or more of small amounts of pre-injection or pilot injection prior to main injection by executing a plurality of times of electricity conduction to the electromagnetic valve of the injector, by inputting fuel pressure immediately before starting actual injection of preceding injection such as pre-injection or pilot injection and immediately before stating actual injection of succeeding injection such as main injection, injection time period of preceding injection and injection time period of succeeding injection are calculated. Or, as shown by a timing chart of FIG. 7, electricity conducting time of the injector drive signal for succeeding injection such as main injection executed after preceding injection such as pre-injection, that is, main injection time is calculated by adding an interval correction amount calculated by using a two-dimensional map of a non-injection interval between the pre-injection and the main injection (play interval) and fuel pressure in the common rail, to basic injection time calculated by a main injection amount (QM) which is set by the engine revolution speed and the command injection amount and the fuel pressure (Pc) in the common rail detected by a fuel pressure sensor.
However, there is a case in which depending on an engine operating condition or operating mode, an error between an actual main injection amount actually injected to supply into the cylinder of the engine and the aimed main injection amount (QM) is increased by only calculating the injection time period of preceding injection and the injection time period of succeeding injection by inputting fuel pressure immediately before starting actual injection of preceding injection such as pre-injection or pilot injection and immediately before starting actual injection of succeeding injection of main injection, further, adding the interval correction amount calculated by play interval and fuel pressure in the common rail during the basic injection time for main injection. As a result of intensive research on the cause, the applicant has found that the higher the combustion chamber pressure (pressure in cylinder) of the engine relative to standard combustion chamber pressure in a case in which preceding injection is not executed at a time point of starting actual injection of main injection, the larger the error between the actual main injection amount and the aimed main injection amount (QM) tends to increase.
According to the common rail fuel injection system, when fuel is injected, the injection amount of the injector is controlled by calculating from a characteristic map formed by calculating a relationship between the fuel injection amount and an injection time characteristic which is set in accordance with the engine operating condition previously by experiment and by outputting an injection command pulse to the injector.
Here, the characteristic map for calculating the fuel injection amount and the injection time characteristic is a map showing the relationship between the fuel injection amount and the injection time by assuming (predicting) fuel injection at predetermined angle at a vicinity of TDC of the engine. Further, although the injection time characteristic is influenced by combustion chamber pressure for injecting fuel and the common rail pressure, since a range used by single injection of the related art is disposed at a vicinity of TDC of the engine adapting the injection time characteristic to the fuel injection amount, the influence of the combustion chamber pressure can be disregarded.
However, in order to achieve a regulated value of exhaust gas of a vehicle mounted with a diesel engine in recent years, there has been developed an injection rate control called as multi-injection, in which fuel is injected in a plurality of times during one combustion cycle of the engine. When such multi-injection is carried out, fuel is injected in a plurality of times over a broad range before and after TDC of the engine and therefore, combustion chamber pressure at a vicinity of TDC of the engine in adapting the fuel injection amount and the injection time characteristic and combustion chamber pressure in starting fuel injection actually differ from each other. Further, the combustion chamber pressure of the engine generally becomes a low value before and after TDC of the engine with a vicinity of TDC of the engine as a top point. Thereby, the fuel injection amount and the injection time characteristic are changed by receiving a change in the combustion chamber pressure and there poses a problem that the actual fuel injection amount is dispersed relative to the respective fuel injection amount of multi-injection set in accordance with the engine operating condition and fuel with a correct value cannot be injected.
It is an object of the invention to provide a fuel injection system capable of restraining an error of a fuel injection timing or a fuel injection amount caused by a change in a combustion chamber pressure.
It is another object of the invention to provide a fuel injection system capable of realizing a target fuel injection amount in a succeeding injection.
It is further another object of the invention to provide a fuel injection system capable of realizing a target fuel injection timing in a respective fuel injection of multi-injection.
It is further another object of the invention to provide a fuel injection system capable of realizing a target fuel injection amount in a respective fuel injection of multi-injection.
According to the invention, by providing correction data storing means for storing correction data formed by calculating a relationship between a combustion chamber pressure of an internal combustion engine and an engine operating condition and an injection mode of a preceding injection influencing on an actual injection start timing of a succeeding injection carried out successively to the preceding injection carried out precedingly in carrying out a multi-injection for supplying to inject a fuel into a cylinder of the engine in a plurality of times by carrying out electricity conduction to an injector in a plurality of times during a compression stroke and an expansion stroke of the engine previously by an experiment, an electricity conduction time period of an injector drive signal for the succeeding injection can be corrected based on the correction data stored by the correction data storing means. Thereby, by reflecting the influence of the combustion chamber pressure of the engine brought about by the preceding injection carried out precedingly prior to the succeeding injection in a correction amount of an electricity conduction time period of an injector drive signal for the succeeding injection, an accuracy of injection amounts at a second stage and thereafter in carrying out the multi-injection can be promoted.
According to the invention, the correction data storing means is characterized in storing the correction data formed by calculating a relationship of the actual injection start timing of the succeeding injection carried out successively to the preceding injection carried out precedingly with any one or more of the combustion chamber pressure of the engine, an engine load or an engine revolution speed or a fuel pressure or a command injection amount and any one or more of an injection amount of the preceding injection or an injection time period of the preceding injection or a noninjection interval between the preceding injection and the succeeding injection or an injection start timing of the succeeding injection previously by an experiment.
According to the invention, by providing combustion chamber pressure predicting means for predicting the combustion chamber pressure of the engine by the engine operating condition of the engine and the injection mode of the preceding injection influencing on the actual injection start timing of the succeeding injection carried out successively to the preceding injection carried out precedingly in carrying out the multi-injection for supplying to inject the fuel into the cylinder of the engine in a plurality of times by carrying out electricity conduction to the injector during the compression stroke and during the expansion stroke of the engine in a plurality of times, the electricity conduction time period of the injector drive signal for the succeeding injection can be corrected based on the combustion chamber pressure predicted by the combustion chamber pressure predicting means. Thereby, by reflecting the influence of the inner cylinder pressure brought about by the preceding injection carried out precedingly prior to the succeeding injection in the correction amount of the electricity conduction time period of the injector drive signal for the succeeding injection, the accuracy of the injection amounts at the second stage and thereafter in carrying out the multi-injection can be promoted.
According to the invention, by providing combustion chamber pressure detecting means for detecting the combustion chamber pressure influencing on the actual injection start timing of the succeeding injection carried out successively to the preceding injection carried out precedingly in carrying out the multi-injection for supplying to inject the fuel into the cylinder of the engine in a plurality of times by carrying out electricity conduction to the injector in a plurality of times during the compression stroke and the expansion stroke of the engine, the electricity conduction time period of the injector drive signal for the succeeding injection can be corrected based on the combustion chamber pressure of the engine detected by the combustion chamber pressure detecting means. Thereby, by reflecting the influence of the combustion chamber pressure brought about by the preceding injection carried out precedingly prior to the succeeding injection in the correction amount of the electricity conduction time period of the injector drive signal for the succeeding injection, the accuracy of the injection amounts at the second stage and thereafter in carrying out the multi-injection can be promoted.
According to the invention, in carrying out the multi-injection for carrying out a small amount of a pilot injection or a pre-injection before carrying out a main injection which can constitute an engine torque at, for example, a vicinity of a top dead center, the inner cylinder pressure at the actual injection start timing of the main injection as the succeeding injection tends to increase more than the combustion chamber pressure of a standard engine when the engine is not influenced by the preceding injection. Hence, by setting the electricity conduction time period of the injector drive signal for the succeeding injection to be shorter in accordance with a degree of increasing the combustion chamber pressure influencing on the actual injection start timing of the succeeding injection than the combustion chamber pressure of the standard engine when the combustion chamber pressure is not influenced by the preceding injection, a variation in the injection amount relative to an aimed injection amount can be restrained.
According to the invention, by applying the injector drive signal to needle driving means, high pressure fuel supplied into a pressure control chamber is overflowed to a low pressure side of a fuel system. Thereby, a nozzle needle overcomes urge force of needle urging means to thereby open the nozzle needle. Further, according to the invention, the invention is characterized in that the succeeding injection is the main injection which can constitute the engine torque at a vicinity of the top dead center and the preceding injection is a small amount of the pilot injection or the pre-injection carried out before carrying out the main injection. Further, according to the invention, the invention is characterized in that the preceding injection is the main injection which can constitute the engine torque at a vicinity of the top dead center and the succeeding injection is a very small amount of an after injection or a post-injection carried out after carrying out the main injection.
According to the invention, a basic injection time period of a respective fuel injection of the multi-injection is calculated by a map or an equation showing a relationship between a fuel injection amount and an injection time period set by assuming (predicting) fuel injection at a predetermined angle at a vicinity of the top dead center of the engine. Further, an injection start angle in starting the respective fuel injection of the multi-injection is calculated from the injection timing and the above-described basic injection time period set in accordance with the engine operating condition. Further, the combustion chamber pressure in starting the respective fuel injection of the multi-injection is calculated by a map or an equation showing a relationship between the injection start angle and the combustion chamber pressure.
Further, by correcting the basic injection time period of the respective fuel injection of the multi-injection in accordance with an amount of a change in the combustion chamber pressure between the combustion chamber pressure calculated based on the injection start angle and the assumed combustion chamber pressure assumed in calculating the basic injection time period, in the respective fuel injection of the multi-injection for injecting the fuel in a broad range before and after the top dead center of the engine, the respective fuel injection amount of the multi-injection set in accordance with the engine operating condition can correctly be injected. Further, in injection time period determining means, the basic injection time period of the respective fuel injection of the multi-injection may be calculated by adding fuel pressure detected by fuel pressure detecting means.
According to the invention, by calculating a correction amount of the injection amount by taking into consideration, the amount of the change in the combustion chamber pressure in starting the respective fuel injection of the multi-injection between the combustion chamber calculated based on the injection start angle and the assumed combustion chamber pressure assumed in calculating the basic injection time period by adding suction pressure detected by suction pressure detecting means to the calculated value of the combustion chamber pressure in starting the respective fuel injection of the multi-injection, in the case of carrying out the multi-injection for injecting fuel in a broad range before and after the top dead center of the engine, a dispersion between the command injection amount set in accordance with the engine operating condition and a total injection amount produced by adding the respective fuel injection amounts of the multi-injection can be restrained.
According to the invention, a fuel pressure correction coefficient is calculated from fuel pressure immediately before the respective fuel injection of the multi-injection. Further, the invention is characterized in that the injection amount corrected by the inner cylinder pressure of the respective fuel injection of the multi-injection is constituted by a value produced by multiplying the correction amount of the injection amount by the calculated fuel pressure correction coefficient. Thereby, the effect of the invention can further be promoted.
According to the invention, the effect of the invention can further be promoted by calculating a final correction injection amount of the respective fuel injection of the multi-injection by adding the injection amount corrected by the combustion chamber pressure to the respective fuel injection amount of the multi-injection set by the injection amount controlling means. Further, according to the invention, the effect of the invention can further be promoted by calculating a final injection time period of the respective fuel injection of the multi-injection by adding the fuel pressure immediately before the respective fuel injection of the multi-injection and the injection amount corrected by the combustion chamber pressure to the basic injection time period of the respective fuel injection of the multi-injection set by injection time period determining means.